This invention relates to a system provided with a main processing part and an interrupt processing part, and more particularly to a self-monitoring system of this type which is so structured that each of these two parts monitors the operations of the other.
Many systems incorporating a computer (and more particularly a micro-computer) are comprised of a central processing unit CPU and peripheral devices which are disposed around this CPU and perform various operations by transmitting signals to the CPU and/or receiving signals from the CPU. The CPU may also contain within itself a device which is independent of the programs stored in the computer and performs operations on such programs.
If such a device which is either external to the computer or forms its internal part issues a command during the course of an operation of the system to temporarily stop the execution of the internal program of the computer and to execute a different independent program, such a routine is referred to as an interrupt, and the program which is executed by an interrupt is referred to as an interrupt processing program. The program which was interrupted may be referred to as the main program. When the execution of an interrupt processing program is completed, the execution of the main program is resumed from the address where its execution was earlier interrupted.
With fluid injection pumps and the like provided with a main processing part which executes a main program and an interrupt processing part which executes an interrupt processing program, the main and interrupt processing parts normally operate independently of each other without affecting each other except when data are exchanged between them. For this reason, if either of them stops functioning completely or begins to operate erratically due to a system abnormality, such an abnormal situation may not be detectable, if observed from outside the system. Let us consider a situation, for example, where it has become impossible for an interrupt to occur at all. In this case, the system will continue to operate only with the main processing part but since the system operation is continuing with the main processing part, it may appear as if the system were operating normally, that is, the abnormality which has occurred and is preventing the interrupt from functioning is not reported by the system. For example, the system may have developed a runaway situation. Such a situation must be prevented, especially in the case of a medical system but it may take a long time before its occurrence is detected.